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Given the following information, what is the minimum vertical clearance of the obstacle by the Performance Class B aeroplane?

Cloud base: 300 ft above reference zero No wind
TAS: 101 kt
Obstacle at 15000 ft from the end of TODR with a height of 600 ft above reference zero
All Engines Rate of Climb (ROC) at Take-Off Power: 1830 ft/min
Single Engine Rate of Climb (ROC) at Take-Off Power: 400 ft/min
Take-Off Power can be used throughout the whole climb segment

  • A
    815 ft
  • B
    215 ft
  • C
    245 ft
  • D
    40 ft
Considerations Performance Class B:
  • From 50 ft to the cloud base, the gradient = all-engine gradient x 0.77;
  • The critical power unit is assumed to become inoperative at the point where visual reference is lost for obstacle avoidance (cloud base).

  • ROC to climb to the cloud base:
    ALL Engine ROC = 1 830 ft/min
    Net all-engine) = 1 830 ft/min x 0.77 = 1 409 ft/min
  • ROC from cloud base to obstacle:
    OEI ROC: 400 ft/min


FIRST STEP:
1) Calculate the Time to climb to 300 ft (beginning at 50 ft screen) = 250 ft / 1 409 fpm = 0.177 min
2) Determine the distance covered in 0.177 min = 0.177 min x 101 kt / 60 min = 0.298 NM x 6 076 = 1 810 ft

At this point, distance to obstacle from the cloud base = 15 000 ft - 1 810 ft = 13 190 ft
1 NM = 6 076 ft; 13 190 ft = 2.17 NM


SECOND STEP:
1) Calculate time to cover 2.17 NM = 2.17 NM / 101 kt x 3 600 s = 77.3 s
2) Height climbed in 77.3 s = 77.3 s x 400 fpm / 60 = 515 ft
Total height climbed = 300 ft + 515 ft = 815 ft
Obstacle clearance = 815 ft - 600 ft = 215 ft

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